The present invention relates to a method as defined in the preamble of claim 1 for controlling a spraying apparatus, especially A spraying apparatus designed for the humidification of the intake air of a piston engine.
The invention also relates to an apparatus as defined in the preamble of claim 14.
The exhaust gases of piston engines, in particular diesel engines, contain many kinds of noxious combustion products. At the high combustion temperatures, the combustion process in the cylinders of a piston engine produces nitrogen oxides (NOx), which are emitted together with the exhaust gases into the atmosphere. Because of the harmful environmental effects of nitrogen oxide emissions, efforts are undertaken to minimize their production.
As is known, adding water to the combustion process reduces the generation of nitrogen oxides. This phenomenon is based on the cooling effect of water. In practice, the introduction of water into the combustion process is often implemented by injecting water into the intake air. These arrangements are advantageous in respect of efficiency of the engine. The maximum amount of water introduced into the combustion space of the engine may advantageously be that amount which will remain in gaseous form in the intake air pressure and temperature conditions.
The object of the invention is to achieve a completely new type of control system that allows the intake air to be humidified in a desired manner in different engine load conditions.
Another object of the invention is to achieve a control apparatus that allows the humidification of intake air in different engine load conditions.
The method of the invention is characterized in that, in accordance with the control system's instructions, when the required amount of water to be supplied through the nozzles increases, liquid flow passages are opened for more nozzles and/or the liquid flow is directed to a nozzle that permits a larger liquid flow through it per unit of time, and when the required amount of water to be supplied through the nozzles decreases, liquid flow passages are closed at least for some of the nozzles and/or the liquid flow is directed to a nozzle that permits a smaller liquid flow through it per unit of time.
The method of the invention is additionally characterized by what is stated in claims 2-13.
The apparatus of the invention is characterized by what is stated in claims 14-25.
The solution of the invention has numerous significant advantages. By applying the method of the invention, a very accurate control of a spraying apparatus can be easily achieved using a relatively economical pump unit. By providing the spraying head with nozzles having different properties, the amount and/or characteristics of the water mist to be injected can be varied in a desired manner by opening and closing the medium channels leading to different nozzles in the spraying head. By providing a constant-output pump and a return line whose k-value always corresponds to the k-values of the closed nozzles, a system is achieved in which the sum of the k-values is always substantially constant. By using a pressure medium to control the valves in the return line, the number of solenoid valves needed can be reduced. The pressure medium used for the control of the return line valves and/or a second pressure medium can be circulated to the nozzles to keep them clean when no liquid to be injected is passed through them.